The invention relates to a light emitter-receiver device and its application to a system for the optical reading of a recording medium.
The invention can be applied especially to the reading of optical disks and relates to the optical system of reading known in the prior art as the optical pick-up technique.
An optical pick-up system consists of:
a downline part combining the optical focusing system and the actuators enabling this optical system to be shifted so that the track being read is followed radially and in focusing; PA1 an upline part combining the write/read laser sources; PA1 at least one splitter enabling the return beam to be redirected to the detectors; PA1 optical means for the concealment or deformation of the beam enabling the detectors to extract the read signals, focusing error signals and track following error signals.
The laser component or components are generally made on a substrate of gallium arsenide while the detectors are made on a silicon substrate.
The invention relates first of all to the upline pick-up part. It reduces the number of components and simplifies the adjusting operation by integrating the detector function into the laser chip.
It is also known that a component made on a gallium arsenide substrate may form a detector: in the field of telecommunications, this property has been used to make alternating two-way communications (half duplex communications). The laser diode is then either forward biased so as to emit light or reverse biased so as to give a photocurrent proportional to the light received. In the field of optical reading pick-ups, it has been proposed to make profitable use of the fact that the light reflected on a disk is refocused with precision on the source to read the information by modification of the current induced to the laser. This method has never been used to make truly operational systems for the quality of the signal in forward bias is insufficient and because there have been no means enabling the extraction of the focusing and track following signal.